<!DOCTYPE html>
<style>
#target {
  width: 200px;
  height: 200px;
  background-color: green;
  /* Data URL access is OK. */
  -webkit-mask-image: url('data:image/svg+xml;utf8, \
    <svg xmlns="http://www.w3.org/2000/svg" width="200px" height="200px"> \
      <rect x="50px" y="50px" width="100px" height="100px" fill="black" /> \
    </svg>');
}
</style>
<div id="target"></div>
